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Digestion

Food is broken down into small molecules
- barrier and immune function

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Absoprtion

Small molecules move frim walls of GI into circulation

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Transport

In circulation and to cells

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Metabolism

In the cell, the chemical reactions that occur to molecules so they can be utilized

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Why do we eat?

-hunger
-appetite

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Hunger

A physiological process that prompts us to find and eat food

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Appetite

A psychological desire to eat specific foods, from environmental stimulu
- smell, sight, sound ( marketing and presentation of food)
- social cues: certain location/activities, feelings

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Satiety

The feeling of being full

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What prompts hunger and satiety?

- signal to the hypothalamus
• nerve cells/stretch receptors
• hormones
- food bulk: bulk (fiber and water), protein and fat, and eating slowly can promote satiety

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Hormones that promote hunger and satiety

-low blood glucose levels trigger glucagon (signals hunger)
-ghrelin (signals hunger)
-Cholecystokinin (signals satiety)

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Ancillary organs

-pancreas
-liver
-gallbladder

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Mechanical digestion

Muscle action and movement

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Chemical digestion

Reaction and secretion
- hydrolysis: break down of compounds with the addition of water
- enzymes: proteins that speed up chemical reaction, unchanging in the process (-ase)
-hormones: chemical messengers that travel to target cells, which then carry out a targeted response

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Saliva contains...

-mucus: that lubricates and moistens food
-antibodies and lysozyme (enzyme): defend against bacteria
-chemicsl digestion: amylase to break down starch

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Esophagus

- anatomy
• connects mouth and stomach: 10 inches long
• epiglottis: prevents food from getting lodged in trachea
-muscle action: peristalsis and gravity
- passes lower esophageal sphincter into the stomach

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Stomach anatomy

- empty is about 3/4 of a cup large
-reservoir that can hold up to about 4 cups

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Stomach: muscle action

-peristalsis
-mechanical digestion by miscle layers: grinds, churns, mixes
-chyme: semiliquid mass mixed with gastric secretions
• chyme leaves stomach via phyloric sphincter 1-4 hrs after eating

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Stomach secretion: gastic juice

-HCl
-pepsinogen/pepsin
-gastric lipase
-intrinsic factor

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HCl

- release stimulated by the hormone gastrin
-denatures protein- chemical digestion
-kills bacteria
-activates enzymes

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Pepsinogen

-inactive protein enzyme
-activated to pepsin (active pepsin enzyme) by HCl
-starts protein digestion -chemical digestion

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Gastric lipase

- fat digestion begins, small amount occurs - chemical digestion

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Intrinsic factor (IF)

Protein needed for absorbtion of vitamin B12

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GI Problems: gastro-esophageal reflux disease (GERD)

-weakened LES
-some contributors: smoking, overweight large high fat meals, spicy, and acidic foods, caffeine, chocolate, alcohol, lying down after a meal
-treatment: diet, antacids, other drugs to reduce HCl production

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Segmentation

A muscle movement action that helps movement of food in the small intestine

- churning and mixing and moving the food up and down as well so its well mixed

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Small intestine: anatomy

- food stays 3-10 hrs in SI
- duodenum: 1'
• connected to stomach via pyloric sphincter
- jejunum: 4-5'
- Ileum: 4-5'
• connected to large intestine via ileocecal valve
- very folded interior

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Small intestine: muscle action

Peristalsis and segmentation

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Where is nutrients absorbed the most in thr small intestine??

Duodenum and jejunum

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Small intestine secretions

- secretions received from:
• pancreas, gallbladder and liver, intestinal cells
- hormones secretred from small intestine to target organs

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Pancreas makes ______ for digestion

- bicarbonate: nuetralize contents, enzymes can function
- enzymes: amylase, protease, lipase

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Liver makes _____ for digestion.

Produces bile, an emulsifier for fat ansorption
- other major nutrient related jobs too

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The gallbladder stores ____ for digestion

Stores and secretes bile

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Intestinal cell enzyme secretions

- cells of the SI produce brush border enzymes
• specific protease
• lipase
• specific sugar enzymes (sucrase, maltase, lactase)

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Secretin signals....

- the stomach to slow gastric emptying
- the pancreas to secrete panceatic bucarbonate

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Chilecystokinin (CCK) signals...

- the gallbladder to release bile
- the pancrease to release pancreatic enzymes
- the stomach to slow gastric emptying
- satiety

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Gastric inhibitory peptide(GIP) signals...

- the stomach ti slow gastric emptying
- the pancreas to increase insulin release

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Large intestine/ colon

- undigested/ unabsorbed matter passes through ileocecal valve to the large intestine
• water, undigested/ unabsorbed residues - fibers, sloughed cells, bacteria, non-food items

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Bacteria in the large intestine/colon

- 90 trillion bacterial cells
- finish digestion and make
• short chain fatty acids- used by colon cells
• vitamin K
• B12 that the bacteria use- not absorbed
• gas
- prebiotics: feed the bateria
- probiotics: replace the bacteria

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Large intestine: muscle action and movement

Peristalsis

- food may stay in LI FOR 12-24 hrs

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Absorption

- absorption: passing of nutrients from thr GI tract into circulation
- most absorption occurs in thr SI
• stomach: some water, alcohol, fluoride
• large intestine: water, short chain fatty acid, vit K
- SI: heavily folded tissue called mucosal membrane
• 500x increase surface area = increase absoption
• within folds fingerlike projections called villi
• villi contains absoprtive cells called enterocytes
• each enterocytes contain microvilli (brush border)

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Passive/simple diffusion

Solutes travel from a high to a low concentration

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Facilitated diffusion

Carrier protein facilitates, high to low

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Active transport

Carrier protein and energy, solutes can travel from a low to a high concentration

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Endocytosis (pinocytosis)

Active transport by which a small amount of intestinal contents is engulfed by the cell membrane into the cell

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SI into circulation: nutrieny transport

- nutrients travel to the blood or lymph for distribution to other cells
- each villus contains capillaries (smallest blood vessel) and lacteal (lymph vessel)
- nutrients cross over into these system

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Nutrient transport: Cardiovascular system

- nutrients cross over into capillaries in villa ---> hepatic portal vein ---> to the liver for storage, utilization or back into curculation

- water-soluble nutrients (protein, carb, some vits, small fatty acids)

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Nutrient transport: lymphatic system

- nutrients cross into lacteals in villi ---> transported to larger lymph vessels ---> drains into circulation by the heart ---> the curculation and liver

- larger fat soluble nutrients

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Metabolism

- the sum of all chemical processes involved in maintaining life

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Anabolism

Build up molecules and use energy

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Catabolism

Break down molecules and release energy